Steam generator

ABSTRACT

A shell and tube steam generator having a U-shaped tube bundle and a preheater. The preheater is disposed on the cold leg portion of the tube bundle and is cooperatively associated with an annular chamber formed by a tube bundle wrapper and the shell to direct inlet water upwardly through the preheater portion and downwardly through the annular chamber, across the tube sheet and upwardly along the outside surfaces of the tubes to optimize the temperature and pressure of the steam produced.

United States Patent Bennett Apr. 16, 1974 STEAM GENERATOR 3,547,08412/1970 Sprague 122/32 {75] Inventor: Robert R. Bennett, Tampa, Fla.Primary Examiner Knneth w. p g

[73] Assignee: Westinghouse Electric Corporation, Attorney, Agent, orFirm-Fred J. Baehr, Jr.

Pittsburgh, Pa.

22 Filed: Feb. 9, 1972 [57] ABSTRACT App]. No.: 224,804

A shell and tube steam generator having a U-shaped tube bundle and apreheater. The preheater is disposed on the cold leg portion of the tubebundle and is cooperatively associated with an annular chamber formed bya tube bundle wrapper and the shell to direct inlet water upwardlythrough the preheater portion and downwardly through the annularchamber, across the tube sheet and upwardly along the outside surfacesof the tubes to optimize the temperature and pressure of the steamproduced.

6 Claims, 4 Drawing Figures STEAM GENERATOR BACKGROUND OF THE INVENTIONThis invention relates to steam generators for nuclear power plants andmore particularly to such steam generators having a preheater portiondisposed therein.

In a steam generator utilizing a heated fluid to produce steam thepressure of the steam is a function of the log means temperaturedifference (LMTD) of the two fluids. Thus, by increasing the LMTD thepressure of the steam can be increased.

An obvious way to increase the LMTD is to raise the temperature of theprimary fluid, however in nuclear steam generating systems thetemperaure of the primary fluid is a limiting factor in the design ofthe system and is normally set at the maximum allowable safe value.

Increasing the LMTD may also be accomplished within the steam generatorby providing a preheater chamber in which inlet water is heated to atemperature lower than the boiling point.

SUMMARY OF THE INVENTION In general a steam generator utilizing aprimary heated fluid to vaporize a secondary liquid, when made inaccordance with this invention, has a vertical shell portion, a tubesheet disposed adjacent one end thereof, a tube bundle having aplurality of U-shaped tubesthrough whichthe primary fluid flows, awrapper encircling the tubes and forming an annular chamber between thetube bundle and the shell, and a preheated portion disposed adjacent thetube sheet. A fluid inlet nozzle is disposed to feed secondary fluidinto the preheater portion and the preheater has an outlet disposed todischarge the secondary fluid into the annular chamber. The wrappercooperates with the shell and outlet to cause preheated secondary fluidto flow generally upwardly over all of the outer tube surface disposedoutside of the preheater.

BRIEF DESCRIPTION OF THE DRAWINGS The objects and advantages of thisinvention will become more apparent'from reading the following detaileddescription in connection with the accompanying drawings, in which:

FIG. 1 is a vertical sectional view of a steam generator made inaccordance with this invention;

FIG. 2 is an enlarged sectional view taken on line II-II of FIG. 1;

FIG. 3 is an enlarged sectional view taken on line III-' -III OF FIG. 1;and

FIG. 4 is an enlarged sectional view taken on line IVIV of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawingsin detail, FIG. 1 shows a steam or vapor generator 1 having a verticalshell portion 3 and a plurality of U-shaped tubes 5 forming a tubebundle 7 which is disposed within the shell 3. The shell has a lowerportion 9 having one diameter, an upper portion 1 1 having a largerdiameter and a frustoconical portion 13 serving as a transition memberbetween the upper and lower portions 11 and 9, respectively. The lowerportion of the shell 9 is enclosed by a spherical head portion 15. Thehead portion 15 has an integral tube sheet 17 which receives the ends ofthe U-shaped tubes 5. A dividing plate 19 separates the head 15 into twogenerally equalcompartments 21 and 23. The inlet compartment 21, the oneon the left, has an inlet nozzle 25 for primary fluid and the outletcompartment, 23, the one on the right, has an outlet nozzle disposedtherein, however, the outlet nozzle is not shown. A sleeve or wrapperportion 27 enwraps the tube bundle and forms an annular chamber 29between the wrapper 27 and'the shell 3. A preheater portion 31' isdisposed adjacent the tube sheet 17 on the cold leg portion of the tubebundle 7, the portion shown on the right. The preheater 31 is anenclosed chamber formed by aportion of the wrapper 27, a bottom circularclosure plate 33 disposed adjacent andparallel to the tube sheet 17, anupper closure plate 34disposed parallel to the bottom closure plate 33and a vertical closure plate 36 extending between the bottom and upperclosure plates 33 and 34, respectively, and parallelto the tubes 5.'Asecondary fluid or water inlet nozzle 37 is disposed in the shell 3adjacent the preheater 31 and has a liner 41 which directs the inletwater to the preheater and an impact plate 43 which directs the inletflow downwardly and prevents the high velocity inlet fluid fromimpinging upon the tubes. A- plurality of horizontal baffles 45 are sodisposed within the preheater 31 to cause the inlet secondary fluid tofollow a sinuous path as it flows upwardly to outlet portion 47, whichdischarge the preheated secondary fluid into the annular chamber 29. Theend of the wrapper 27 adjacent the tube sheet 17 has a plurality ofnotches 49 so disposed to direct the preheated fluid so that it sweepsacross the tube sheet 17 prior to flowing upwardly along the outersurface of the tubes not contained'within the preheater. Some of thenotches 49 are provided with adjustable flow gates 51 which are adaptedto change the opened area of the notches to adjust the flow of thepreheated secondary fluid across the tube sheet.

The wrapper 27 generally parallels the shell and flares outwardly alongwith the transition portion 13 and has a domed end closure 53 disposedin the lower portion of the upper portion 11 of the shell 3. The domedend closure 53 and wrapper 27 thus form a chamber 55 above the tubes forcollecting the steam or vaporproduced by the steam generator. The upperportion 11 of the shell is closedby an elliptical head portion 57. Asteamor vapor outlet nozzle 59 is centrally disposed in the ellipticalhead and provides a discharge port for vapor produced in the steamgenerator. Two diametrically opposed manways 61 provide access to theinterior of the upper portion of the shell which houses two separatemoisture or liquid separators 63 and 65. The first separator 63 is acentrifugal-type separator and comprises a plurality of riser tubes 67in communication with the chamber 55 and extending upwardly from thedomed end portion 53 of the wrapper 27. The riser tubes 67 'have swirlvanes 69 disposed therein. The swirl vanes 69 extend radially from acentrally disposed hub portion 71 which is disposed adjacent the upperend of the riser tube 67. A closure plate 73 generally extendshorizontallyacross the shell 3 dividing the upper portion 11 into twochambers. The closure plate 73 is disposed slightly above the upper endof the riser tubes 67 and has-orifices 75 which register with the risertubes 67. Collars 77 extend through the orifices 75 and extenddownwardly therefrom. Sleeves 79 encircle the riser tubes and dependfrom the closure plate 73. The lower end of the sleeve 79 are disposedabove the dorned end closure 53 providing a lower discharge port. Theupper end of the sleeves have tangential discharge ports 81 disposedadjacent the closure plate 73.

The second moisture separator 65 comprises two groups of hook and pocketvane-type or chevron separators disposed in parallel, one group beingdisposed above the other. The hook and pocket vane-type separators 65have drip legs 83 depending therefrom, the lower end of the drip legs 83have a seal cup 85 connected thereto.

The operation of the steam generator is as follows: primary heated fluidfrom a nuclear reactor (not shown) flows through the primary fluid inletnozzle to the inlet chamber 21, which acts as a header for the U-shapedtubes. The primary fluid then flows through the U-shaped tubes and isdischarged into the outlet chamber 23 and returns to the nuclear reactorthrough the discharge nozzle (not shown). Secondary fluid or waterenters through the secondary fluid inlet nozzle 37 and flows to thepreheater section 31 wherein it flows upwardly across the cold legportion of the tube bundle following a sinuous path defined by thebaffles 45 to the outlet ports 47 disposed in the upper end of thepreheater. The preheated secondary fluid or water then flows downwardlyin the annular chamber 29 and is directed to sweep across the tube sheet17 by the notches 49. The open area of the notches 49 is adjusted by theflow gates 51 to provide the proper distribution of secondary fluidsweeping across the tube sheet to prevent chemical hideout and prematureboiling. The secondary fluid then flows upwardly over the outer surfaceof the tubes not disposed within the preheater removing heat from theprimary fluid thus increasing its temperature to the boiling point.Boiling takes place as the secondary fluid moves upwardly, thus formingsteam or vapor which separates from the liquid and collects in thechamber 55. The steam which collects in the chamber 55 flows upwardlythrough the riser tubes 67 and as it passes over the swirl vane 69 itbegins to swirl and form a vortex as it leaves the riser tubes. Themoisture or liquid flows to the outside of the vortex and is dischargeddownwardly through the annular chamber formed between the sleeve and theriser tube or is discharged through the tangential discharge nozzles 81disposed adjacent the closure plate 73. Steam-with a large portion ofthe moisture removed then flows upwardly through the collar 77 andthrough the hook and pocket vane-type separator 65 which removesadditional moisture or fluid droplets from the vapor or steam and thenessentially moisture-free vapor or steam flows through the outlet nozzle59. The water or liquid droplets separated from the steam are dischargedinto the lower portion ofthe upper portion of the shell and flow acrossthe upper side of the domed enclosure 53 and down the annular chamber 29and mixes with the discharge from the preheater. The mixture flowsdownwardly due to natural circulation and sweeps across the tube sheetprior to beginning its upward flow along the outside of the tubes notincluded in the preheater.

The steam generator 1 with a preheater 31 as hereinbefore describedadvantageously raises the temperature of the secondary fluid to atemperature below the boiling point and then'directs the preheated fluidupwardly along the outer surfaces of the tubes not included within thepreheater to optimize the pressure and temperature of the steam producedtherein.

What is claimed is:

1. A vapor generator'utilizing a primary heated fluid to vaporize asecondary fluid, said vapor generator having a vertical shell portion, atube sheet disposed adjacent one end thereof, a tube bundle formed by aplurality of U-shaped tubes through which said primary fluid flows, awrapper generally encircling the entire length of said tube bundle toform an annular chamber between said wrapper and said shell whichgenerally extends the entire length of said tube bundle, a preheatedportion disposed adjacent said tube sheet, and a secondary fluid inletnozzle disposed to feed secondary fluid into said preheater portion,said preheater portion having outlet means for discharging secondaryfluid into said annular chamber, said wrapper being cooperativelyassociated with said shell and said outlet whereby preheated secondaryfluid flows generally upwardly over all the outside surface of the tubesdisposed outside the preheater,

2. A vapor generator as set forth in claim 1, wherein the secondaryfluid nozzle is in fluid communication with a portion of the preheaterdisposed adjacent the tube sheet, whereby the secondary fluid flowsupwardly in the preheater portion.

3. A vapor generator as set forth in claim 1, wherein the tube sheet andpreheater are disposed adjacent the lower end of the shell.

4. A vapor generator as set forth in claim 3, wherein the lower end ofthe wrapper has a plurality of openings disposed therein, wherebypreheated secondary fluid sweeps the tube sheet preventing chemicalhideout and premature boiling adjacent the tube sheet.

5. A vapor generator as set forth in claim 3, wherein the shell hasseparating means disposed therein, said separating means being disposedin the upper portion of the shell and being adapted to remove entrainedsecondary fluid droplets from the vapor produced therein, saidseparating means having drain means connected thereto, for returning thesecondary fluid collected in liquid form to the chamber formed betweenthe wrapper and the shell whereby said liquid mixes with the preheatedsecondary fluid as they are moved down: wardly toward the tube sheet bynatural circulation.

6. A vapor generator as set forth in claim 5, wherein the upper end ofthe wrapper is closed forming a chamber above the upper end of the tubesand the separating means are in communication with said chamber.

1. A vapor generator utilizing a primary heated fluid to vaporize asecondary fluid, said vapor generator having a vertical shell portion, atube sheet disposed adjacent one end thereof, a tube bundle formed by aplurality of U-shaped tubes through which said primary fluid flows, awrapper generally encircling the entire length of said tube bundle toform an annular chamber between said wrapper and said shell whichgenerally extends the entire length of said tube bundle, a preheatedportion disposed adjacent said tube sheet, and a secondary fluid inletnozzle disposed to feed secondary fluid into said preheater portion,said preheater portion having outlet means for discharging secondaryfluid into said annular chamber, said wrapper being cooperativelyassociated with said shell and said outlet whereby preheated secondaryfluid flows generally upwardly over all the outside surface of the tubesdisposed outside the preheater.
 2. A vapor generator as set forth inclaim 1, wherein the secondary fluid nozzle is in fluid communicationwith a portion of the preheater disposed adjacent the tube sheet,whereby the secondary fluid flows upwardly in the preheater portion. 3.A vapor generator as set forth in claim 1, wherein the tube sheet andpreheater are disposed adjacent the lower end of the shell.
 4. A vaporgenerator as set forth in claim 3, wherein the lower end of the wrapperhas a plurality of openings disposed therein, whereby preheatedsecondary fluid sweeps the tube sheet preventing chemical hideout andpremature boiling adjacent the tube sheet.
 5. A vapor generator as setforth in claim 3, wherein the shell has separating means disposedtherein, said separating means being disposed in the upper portion ofthe shell and being adapted to remove entrained secondary fluid dropletsfrom the vapor produced therein, said separating means having drainmeans connected thereto, for returning the secondary fluid collected inliquid form to the chamber formed between the wrapper and the shellwhereby said liquid mixes with the preheated secondary fluid as they aremoved downwardly toward the tube sheet by natural circulation.
 6. Avapor generator as set forth in claim 5, wherein the upper end of thewrapper is closed forming a chamber above the upper end of the tubes andthe separating means are in communication with said chamber.